1. Field of the Invention
The present invention relates to resin compositions for light control sheets. In addition, the invention relates to light control sheets prepared by using such resin compositions.
2. Related Art Statement
It is known from the disclosures of Japanese Patent KOKAI (Laid-open) No. 147405/1989 that a light control sheet can be prepared by a process wherein an UV ray is irradiated onto a photo-polymerizable composition comprising at least two compounds having different refractive indexes. For instance, there are known compositions which contain urethane monomers or oligomers and bromine-containing monomers and the like. Such known compositions may be fabricated into light control sheets having good optical properties.
As mentioned above, the known compositions have good light control properties, but it is still described that a further improvement should be made on such compositions. Generally, the opaque area (i.e. the light-scattering area) of a light control composition, which has been cured, should have a high haze value, and the transparent area of the composition should have a light transmittance of at least 95%. According to the prior art, a cured composition, which met the above-mentioned conditions, inevitably had a thickness of 200 to 300 .mu.m. However, it is highly desired to provide a thinner cured composition for the reasons given below.
Namely, a decrease of the thickness of cured compositions is highly desirable for the following two reasons. Firstly, there is a problem of the polymerization reaction heat generated in a large scale production of light control sheets. In the case of photopolymer sheets, it is recognized that a sheet, having a thickness of 200 to 300 .mu.m, is a relatively thick sheet. In the course of the production of a polymer sheet, there is a polymerization reaction accompanying an instantaneous generation of a large amount of heat, so that there may occur a distortion in the substrate layer or the light control polymer layer of the sheet, and also there may occur a disorder in the structure formed in the sheet and having the characteristic optical properties. It is expected that such a vigorous heat generation and a distortion of cured polymer structure might be eliminated, if the thickness of such a light control sheet is decreased.
Secondly, it is considered that the amount of the composition can be decreased by a decrease of the thickness of the sheet. This gives an economical effect.